Electrical contact terminals of the type used in multi-contact electrical connectors for circuit boards or other substrates are usually manufactured from sheet metal by stamping a flat blank from the sheet metal and then forming or bending the blank to produce the desired final configuration in the terminal including a contact portion and a suitable spring for developing the required contact force when the connector is mated with a circuit board or the like. An alternative type of contact terminal may be produced by simply stamping the sheet metal stock without forming in a manner such that the finished terminal lies in the plane of the original sheet metal stock. Terminals of this type can be described as being complanate in that they are relatively flat and have a thickness which is equal to the thickness of the metal stock from which they were produced. The terminal must be designed such that a spring means is provided to produce the required contact force. Since sheet metal materials are extremely stiff when flexed in their own planes (as opposed to being flexed transversely of their planes), great care must be taken in the design of the terminal to achieve flexure in the self-contained spring means of the terminal. U.S. Pat. Nos. 4,176,895; and 3,215,968 show complanate terminals of the type under discussion and also show how such terminals can be designed to achieve a self-contained spring in the flat terminal for developing the contact force.
The present invention, in accordance with one aspect thereof, is directed to the achievement of an improved flat complanate terminal having self-contained spring means which can be modified to yield a range of contact forces for the finished terminal and/or a pre-selected deflection range. In other words, the invention is directed to the achievement of a flat terminal stamped from metal stock without forming, which can be tailored to use under a wide range of operating conditions.
In accordance with a further aspect thereof, the invention is directed to the achievement of a contact terminal characterized by its having a low and predictable self-inductance characteristic. Every terminal has some inductance effects and under many circumstances these are of little or no significance; for example, where the terminal is used to carry direct current without rapid switching or where the frequency of the alternating current in the circuit is extremely low. However, much modern electronic equipment involves very high frequency alternating current or rapid switching of current in the circuits so that self-inductance effects can be troublesome. Some telephone equipment, for example, has switching times of the order of 10.sup.-9 seconds and under current conditions of these types, the rate of change of the current with time is extremely high notwithstanding the fact that the actual magnitude of the current is relatively low. Such high current change rates then result in self-inductance effects which can, in turn, interfere with the normal operation of the equipment. In general, contact terminals which have sinuous spring portions and a relatively long current path through the contact can prove troublesome from the standpoint of self-induction effects.
One type of contact terminal, in accordance with the invention, is produced by stamping flat sheet metal stock without significant subsequent forming so that all of the parts of the terminal lie in a single plane, the plane of the original sheet metal. The parts of the terminal comprise a yoke portion having extending therefrom a contact arm, a spring arm, and a solder post or the like, for connecting the terminal to other circuits. The contact arm and the spring arm are in side-by-side relationship and a contact portion on one side of the contact arm at its free end engages the terminal pad on a circuit board or other complementary terminal device. A bearing portion is also provided on the end of the contact arm which engages an opposed bearing portion on the end of the spring arm. The contact arm is capable of undergoing flexure when the connector in which the terminal is contained is mated with a complementary part and upon such flexure, the contact arm moves in a direction towards the spring arm. The spring arm is thereby mechanically loaded and stressed so that it develops the necessary reaction force to press the outer end of the contact arm against the circuit board. The spring arm does not serve as a current carrying member, since all of the current flows directly from the contact arm to the solder post and thence to the external circuit. The spring arm can, therefore, be proportioned to perform its purely mechanical function without regard to electrical considerations. The contact arm likewise can be designed and dimensioned with purely electrical considerations in mind and without concern for the matter of spring force.